Weird Object Shape in Solid Mode
Bevel modifier, when applied to the whole of complex meshes in particular,  can mess things up. To avoid this model the shape from a subdivided, 8×8, plane removing undesired vertices/edges. Bevel it, selected vertices only (it's called a vertex group), to obtain rounded corners as shown below. Extrude it when done and remove doubles. 
Use knife project with the cut through enabled for the rounded holes as the rectangular hole is the subdivided faces deleted.